1. The Field of the Invention
The present invention relates to rendering images on display devices having pixels with separately controllable pixel sub-components. More specifically, the present invention relates to filtering and subsequent displaced sampling of image data to obtain a desired degree of luminance accuracy and color accuracy.
3. The Prior State of the Art
As computers become ever more ubiquitous in modern society, computer users spend increasing amount of time viewing images on display devices. Flat panel display devices, such as liquid crystal display (LCD) devices, and cathode ray tube (CRT) display devices are two of the most common types of display devices used to render text and graphics. CRT display devices use a scanning electron beam to activate phosphors arranged on a screen. Each pixel of a CRT display device consists of a triad of phosphors, each of a different color. The phosphors included in a pixel are controlled together to generate what is perceived by the user as a point or region of light having a selected color defined by a particular hue, saturation, and intensity. The phosphors in a pixel of a CRT display device are not separately controllable. CRT display devices have been widely used in combination with desktop personal computers, workstations, and in other computing environments in which portability is not an important consideration.
LCD display devices, in contrast, have pixels consisting of multiple separately controllable pixel sub-components. Typical LCD devices have pixels with three pixel sub-components, which usually have the colors red, green, and blue. LCD devices have become widely used in portable or laptop computers due to their size, weight, and relatively low power requirements. Over the years, however, LCD devices have begun to be more common in other computing environments, and have become more widely used with non-portable personal computers.
Conventional image data and image rendering processes were developed and optimized to display images on CRT display devices. The smallest unit on a CRT display device that is separately controllable is a pixel; the three phosphors included in each pixel are controlled together to generate the desired color. Conventional image processing techniques samples of image data to entire pixels, with the three phosphors together representing a single portion of the image. In other words, each pixel of a CRT display device corresponds to or represents a single region of the image data.
The image data and image rendering processes used with LCD devices are those that have been originally developed in view of the CRT, three-phosphor pixel model. Thus, conventional image rendering processes used with LCD devices do not take advantage of the separately controllable nature of pixel sub-components of LCD pixels, but instead generate together the luminous intensity values to be applied to the three pixel sub-components in order to yield the desired color. Using these conventional processes, each three-part pixel represents a single region of the image data.
It has been observed that the eyestrain and other reading difficulties that have been frequently experienced by computer users diminish as the resolution of display devices and the characters displayed thereon improves. The problem of poor resolution is particularly evident in flat panel display devices, such as LCDs, which may have resolutions 72 or 96 dots (i.e., pixels) per inch (dpi), which is lower than most CRT display devices. Such display resolutions are far lower than the 600 dpi resolution supported by most printers. Even higher resolutions are found in most commercially printed text such as books and magazines. The relatively few pixels in LCD devices are not enough to draw smooth character shapes, especially at common text sizes of 10, 12, and 14 point type. At such common text rendering sizes, portions of the text appear more prominent and coarse on the display device than when displayed on CRT display devices or printed.
In view of the foregoing problems experienced in the art, there is a need for techniques of improving the resolution of images displayed on LCD display devices. While improving resolution, it would also be desirable to accurately render the color of the images to a desired degree so as to generate displayed images that closely reproduce the image encoded in the image data.